CHAPTER X 



THE ACTIVE PRINCIPLES OF THE PARS NEU- 

 RALIS; IS THERE CONVINCING EVIDENCE THAT 

 THE PARS NEURALIS IS A GLAND OF INTERNAL 

 SECRETION? 



NEARLY all the extracts of the pars neuralis which 

 have been used commercially or for scientific in- 

 vestigation have been obtained from the most con- 

 venient source — the posterior lobe of the ox-pituitary." The 

 simpler extracts or the fractions with predominantly vaso- 

 pressor effects usually contain the hormone causing a dif- 

 fusion of the melanosomes. Inasmuch as there is satisfactory 

 evidence that this hormone is derived from the pars inter- 

 media, its presence in posterior-lobe extracts will require no 

 further discussion (see chap. ix). From the pars neuralis it- 

 self, two extracts with different effects have been separated: 

 (i) the oxytocic or uterine-stimulating principle, and (2) the 

 vasopressor principle (elevating the blood pressure, stimu- 

 lating the bowel [particularly the colon], and, depending upon 

 conditions, causing a moderate diuresis or inhibiting a 

 diuresis which would occur otherwise).^ 



THE DISTRIBUTION OF THE ACTIVE PRINCIPLES 



The initial extraction of the active substances of the pars 

 neuralis is a simple procedure. Posterior-lobe tissue, prefer- 

 ably in the form of a powder made by dehydrating and de- 

 fatting the fresh tissue by acetone, is thoroughly mixed with 



' The posterior lobe includes both the pars neuralis and the pars intermedia. 



^On the basis of comparative assays of simple, commercial extracts of the pos- 

 terior lobe Bijlsma, Burn, and Gaddum (1928) concluded that neither the oxytocic 

 nor the pressor principle is responsible for diuresis inhibition. In all subsequent 

 work the vasopressor fraction has been found to cause diuresis inhibition. 



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